Metal-air batteries are a class of electrochemical cells, in which oxygen, typically obtained from the ambient environment, is reduced at a catalytic cathode surface as part of the electrochemical cell reaction. The anode, which is oxidized by releasing electron to the external circuit, is typically based upon Fe, Al, Zn, Mg, or Ca and Li. Lithium-air batteries represents one type of metal-air batteries. Abraham and Jiang (see J. Electrochem. Soc. 143, 1-5 (1996); and U.S. Pat. No. 5,510,209) were the first to report a lithium/oxygen cell with a non-aqueous polymer separator including a film of polyacrylonitrile swollen with a PC/EC LiPF6 electrolyte solution. During the discharge of the cell, oxygen is reduced at the electroactive cathode to produce oxygen ion and/or peroxide ion, which react with lithium ions to generate Li2O2 and/or Li2O, which deposit on the carbon surfaces or in the pores of the electrode.
High surface area carbon materials such as carbon black and acetylene black provide numerous sites for oxygen reduction reaction and deposition of lithium peroxide and/or lithium oxide. In lithium-air batteries, a convention is defined when describing the specific capacity of the cell which uses the capacity per gram of carbon material. Thus, the specific capacity of the lithium-air cell is significantly high; and is typically on the order of 1500-2000 mAh/g of carbon, which compares to a specific number of 120-280 mAh/g for intercalating-type cathode materials for lithium ion batteries. The extremely high energy density makes lithium air batteries a promising candidate for applications in plug-in hybrid electric vehicles (PHEV) and electric vehicles (EV). The difficulty with lithium air technology is in providing practical systems that can operate in real conditions. For example, one of the major obstacles is the corrosion of lithium metal from oxygen and moisture in the atmosphere, which is a significant limitation on use in a wide variety of environments.
As described above, lithium-air batteries are not based on the intercalation mechanism of lithium-ion batteries. The specific capacity of the lithium anode is about 3800 mAh/g, which is about 10 times of the capacity of mesocarbon microbeads (MCMB) used as the negative electrodes for lithium-ion batteries. The positive electrode of the lithium-air batteries is basically a conductive porous carbon electrode, storing the critical and unlimited component of oxygen in air. However, the porous structure and surface of the cathode materials usually lose function due to the occupation of deposits by Li2O2 and/or Li2O from the prior discharge step and unable to decompose in the following process of charging. Due to this, the cycle performance of the cell gradually deteriorates.